Jökull - 01.12.1975, Page 42

Fig. 1. The Arnarvatnsheidi area as defined in the paper. Lakes shown by capital letters G:
Gunnarssonavatn, H: Hagldamóatjörn, M: Mordísarvatn, N: Núpavatn, S: Stóralón, R: Rétta-
vatn.
Mynd 1. Arnarvatnsheiði, eins og hún er mörkuð og rcedd i greininni. G: Gunnarssonavatn, H:
Hagldamóatjörn, M: Mordísarvatn, N: Núpavatn, S: Stóralón, R: Réttavatn.
on the geological map. Strútur, the two Sauda-
fells, Svelti and other unnamed outliers on the
north-west edge of Hallmundarhraun are all of
this formation. Apart from Strútur the other
features are mainly capped by iight-grey sub-
aerial massive basalts and “have clearly formed
under a relatively thin ice cover probably at an
early stage in a glacial cycle” (p. 107).
The author examined a section exposed bv
the Nordlingafljót where it cuts through the
western end of Thorvaldsháls. Here rather well
consolidated tills or tillites are shown on the
steep east bank of the river near the Vopnalág
depression.
It can be suggested that, whatever the pro-
venance of the rocks concerned and their age,
the area is one in which relatively poorly con-
solidated deposits, sedimentary or hyaloclastite,
were originally covered by massive basalts.
From the point of Sudurmannasandfell, some
40 JÖKULL 25. ÁR
distance to the northeast of Fig. 1, a good
picture of the relief of the area can be obtain-
ed. The main features are the steep slope from
the Langijörfi plateau down to Arnarvatn stóra,
the escarpment running along the south shore
of that lake, and minor escarpments facing
north-west running across the landscape, with
rounded hillocks of deposits between them
(Fig. 2). On cross-sections drawn through the
area of Fig. 1 from north-east to south-west
(Fig. 3), it becomes clear that the district lowers
towards the south-west in a series of steep slopes
breaking otherwise relatively level areas.
MORPHOLOGY
Steep slopes and even rock escarpments are
much more common on the ground than avail-
able maps indicate, and a survey of air photo-